(a) Field of the Invention
The present invention relates to a photographic lens system for use in a compact camera having a range finder and using a 35 mm film, and more particularly to a lens system having an angular field of view of 60.degree. to 70.degree. and an aperture ratio of F/2.8, the length from the first lens surface to the film surface being almost as short as the overall focal length.
(b) Description of the Prior Art
Conventionally, for the purpose of making compact a lens system such as described above, a Tessar type lens system with a rear aperture stop has been adopted. However, in a lens system of the Tessar type with a rear aperture stop (as described, for example, in Japanese Published Examined Patent Application No. 19387/72), the length from the first lens surface to the film surface had to be limited to a length in the order of 42 mm for use in a 35 mm film.
In order to eliminate this disadvantage, the inventor of the present application has designed a very compact lens system and has filed it as a Japanese patent application (See Japanese Published Unexamined Patent Application No. 76147/79). In this lens system, the length from the first lens surface to the film surface is made so short as to be about the same as the focal length. However, in this lens system, there has been a space to be more or less improved in respect that the sharpness of the image near the margin of the image plane is somewhat lower than in the central part of the image plane.
The present invention is to provide a very compact photographic lens system wherein the length from the first lens surface to the film surface is not more than 35 mm and various aberrations are well corrected not only in the central part but also in the marginal part of the image plane.
In order to shorten the total length of the lens system, there have been known two methods, one is to shorten the focal length of the lens system and the other is to make the telephoto ratio small (a proportion of the length from the first lens surface to the film surface, to the focal length). In order to make the total length of the lens system markedly short as described above, it is necessary both to shorten the focal length and to make the telephoto ratio small. In order to make the telephoto ratio small, there may be adopted a telephoto type lens system in which a negative lens is arranged in the rear portion of the lens system. However, in order to shorten the focal length in such a telephoto type lens system, it is necessary to secure good lens characteristics over an angular field of view wider than 60.degree. which was inconceivable in a conventional telephoto type lens system.